An artificial marble is superior to a natural marble in that it is light and has high workability. The artificial marble is widely used to produce various top boards such as a floor material, a wall material, a table, a kitchen top board, and a wash bowl as a substitute for a natural marble. As an artificial marble, graceful and high-class texture which resembles a natural stone is required, so that how to realize natural-stone-like texture is an important matter.
As a producing method of the artificial marble, the following method (Japanese Publication of Examined Application No. 24447/1978 (Tokukoushou 53-24447)(publication date: Jul. 20, 1978)) is known: for example, natural rock crushed particles and a heat-curable liquid synthetic resin are sufficiently kneaded so as to produce a mass having proper shape and size, and natural rock powdered particles or pigment whose color is different from that of the foregoing natural rock crushed particles are made to adhere to a surface of the mass, and the mass having one or more than one color tones is put into a mold, and the mass is pressed and cured with heat, so that an artificial marble having lineal patterns is obtained.
Further, the following method (Japanese Unexamined Patent Publication No. 102155/1990 (Tokukaihei 2-102155)(Publication date: Apr. 13, 1990) is known: an artificial marble obtained by curing resin components in which filler has been compounded in advance is crushed into particles of predetermined size with a hammer mill or a roll mill, and the particles and resin components are compounded again, so that an artificial marble which resembles a granite is obtained.
In addition, as another method for realizing a design which resembles a natural stone, the following method (Japanese Unexamined Patent Publication No. 952/1977 (Tokukaishou 52-952)(Publication date: Jan. 6, 1997) is known: natural stone particles and resin particles etc. are compounded into a matrix that is constituted of a resin having transparency and filler, so that an artificial marble having a design which resembles a granite is obtained.
However, when a crushed natural stone is used so as to obtain an artificial marble having a design which resembles a natural stone in a method as in Tokukoushou 53-24447, there occurs such a problem that the workability declines. Further, when the crushed natural stone is used, the crushed natural stone does not sufficiently adhere to a resin, so that exfoliation of an interface tends to occur.
Further, in the case where the natural rock crushed particles and a heat-curable liquid synthetic resin are kneaded so as to produce a mass having proper shape and size, and natural rock powdered particles or pigment whose color is different from that of the foregoing natural rock crushed particles are made to adhere to a surface of the mass, and the mass is subjected to press molding, the mass of the kneaded materials is squashed by hot pressing and floats, so that, as shown in FIG. 2, a border line between the masses, that is, the interface of the masses is vague, and a linear shape is not produced, and the interface itself becomes a flow line.
However, it is difficult to produce an artificial marble having a design which resembles a natural stone by using only resin materials, without using the crushed natural stone.
While, like Tokukaihei 2-102155, in the case where crushed hard resin particles obtained by crushing a cured resin are dispersed over resin, which serves as the matrix, so as to be cured, a molding compound made up of only resin materials is used, so that this does not raise problems such as the decline of the workability and the exfoliation of the interface which occur in the case where the crushed natural stone is used. However, when compounding many crushed had resin particles so as to obtain a desired design, porous crushed hard resin particles absorb monomer component in the resin which serves as the matrix, so that viscosity of the molding compound becomes unsteady; or flowability of the molding compound deteriorates and an arrangement of the crushed hard resin particles is imbalanced, so that an unnatural pattern is formed. Thus, it is difficult to produce an artificial marble having a desired pattern. It is general to compound at most about 30 parts crushed hard resin particles with respect to 100 parts matrix.
Further, also the method recited in Tokukaishou 52-952 raises the foregoing problems, so that it is difficult to produce an artificial marble having a desired pattern which resembles a natural stone, and only a granite-like artificial marble having a monotonous pattern can be obtained.